Krabi, on the mainland across the bay from Phuket, is reachable as a long day trip — most famous for Railay Beach's dramatic limestone cliffs.
What's involved
Typically a combination of road and boat transfer (Railay itself has no road access, reached only by longtail boat), taking a meaningful chunk of the day just in transit — a full-day rather than half-day commitment.
What you'll see
Railay's towering limestone cliffs (a well-known rock-climbing destination in their own right), plus nearby beaches and viewpoints depending on the specific tour itinerary.
Day trip vs staying over
Given the transfer time involved, some travellers choose to stay a night or two in Krabi rather than doing the full round trip in a single day — worth weighing against your remaining time in Phuket before committing to a single-day version.
Booking notes
Weather and sea conditions can affect the boat portion of the journey — check current-season reliability with your tour operator, particularly outside the November-April high season.